Need has long existed for inexpensive, easy-to-produce compositions for grinding tools which are used in the manufacture of articles made from stone such as marble and granite. Such grinding compositions must be easily formed into a solid, dense grinding tool body and must be simple enough to make that workers of ordinary skill can cast the grinding composition in grinding tool molds.
It has been common practice for the abrasive tools used in the manufacture of articles from stone, such as marble and granite, to be manufactured by a casting process using a magnesium oxide-magnesium chloride ("Sorel") cement and abrasive grains. This cement hardens without heating or other special processing. Abrasive grinding tool segments are generally formed by casting, and are attached to a rotating member to form a grinding wheel. This grinding wheel is rotated against the stone being polished or ground, either flooded by water or subjected to flowing water. The water serves to remove the debris resulting from grinding or polishing, to cool the grinding tools, and to prevent their becoming clogged or coated with debris. Because of their exposure to water, the grinding tools are subject to water reaction or dissolution. Therefore, one desirable characteristic of the cementitious phase is water insolubility.
Because the grinding tools are primarily subjected to compressive loads and because the stones being polished or ground are finished to the edge, resulting in the grinding tool passing beyond the edge of the stone, forces are generated which can cause chipping of the grinding tool. Fracture toughness is therefore a highly desirable property of the grinding material.
Because rapid wear of the grinding tool is undesirable, hardness is important. The abrasive grains must be very hard, and a desirable cementitious phase should be somewhat hard, although not excessively hard or brittle. Some flexibility is desirable in the grinding tool, became if the cementitious phase is somewhat flexible, there is less tendency for fracture during operation.
The "Sorel" cementitious material currently being used is lacking in water insolubility, fracture toughness, and flexibility. It is the lack of water insolubility, fracture toughness, and flexibility that the applicants' invention overcomes.